The present invention relates to a diesel particulate trap. More specifically, the present invention relates to a method and apparatus for regenerating a diesel particulate trap using microwave radiation.
Increased regulation has reduced the allowable levels of particulates generated by diesel engines. The particulates can generally be characterized as a soot that is captured and reduced by particulate filters or traps. Present particulate filters or traps contain a separation medium with tiny pores that capture particles. As trapped material accumulates in the particulate trap, resistance to flow in the particulate trap increases, generating back pressure. The particulate trap must then be regenerated to burn off the particulates/soot in the particulate trap to eliminate the back pressure and allow air flow through the particulate trap. Past practices of regenerating a particulate trap utilized an energy source such as a burner or electric heater to generate combustion in the particulates. Particulate combustion in a diesel particulate trap by these past practices has been found to be difficult to control and may result in an excessive temperature rise.
The present invention is a method and apparatus for regenerating a particulate trap using microwave energy. The present invention directs microwaves to select locations in a particulate trap such as near an inlet channel end plug of a particulate trap to initiate regeneration and prevent particulate build-up. By directing microwaves to select locations, a relatively small amount of energy initiates the particle combustion that regenerates the particulate trap. The exotherm or combustion of a small amount of particulates is leveraged to burn a larger number of particulates.
The present invention includes a particulate trap placed in the exhaust flow of a diesel engine. The particulate trap includes microwave-absorbing materials configured to absorb microwaves in selected locations in the particulate trap. A microwave source is operatively coupled to a wave guide, and a focus ring may be used to direct the microwaves to the microwave-absorbing materials. The microwave-absorbing material generates heat in response to incident microwaves to burn off particulates. Materials transparent to microwaves are preferably used for the basic construction of the particulate trap housing and other areas in the particulate trap where it would be inefficient to absorb microwave energy.
In the present invention, the microwave reflecting and guiding materials are configured to guide and reflect the microwaves until they are incident upon the microwave-absorbing material. The microwaves in effect xe2x80x9cbouncexe2x80x9d around the particulate trap until they are incident upon the microwave-absorbing materials. By strategically locating microwave-absorbing materials, microwaves may be used efficiently at the locations they are most needed to initiate the burn off of particulates.
The use of microwaves in the present invention further allows the frequency of particulate trap regeneration to be precisely controlled. The present invention may schedule regenerations based on empirically-generated particulate trap operation data and/or utilize a pressure sensor to determine when the particulate trap requires a regeneration.